EP 0 811 872 and GB 2 313 920 disclose a diffractive spatial light modulator which may be used in a display. The spatial light modulator (SLM) comprises a ferroelectric liquid crystal layer covered on one side by a continuous electrode and on the other side by discrete picture element (pixel) electrodes. Each of the pixel electrodes comprises first and second sets of interdigitated electrodes. By applying suitable voltages to the various electrodes, each pixel can be switched between a non-diffractive state, in which light is transmitted or reflected into the zeroth order diffraction mode, and a diffractive state in which the pixel forms a phase-only diffraction grating and diffracts light into non-zero diffractive orders. In the diffractive mode, each pixel comprises a plurality of elongate or strip regions such that light beams passing through adjacent strip regions undergo a relative phase shift of 180 degrees. In the non-diffractive state, all light passing through the pixel is subject to substantially the same phase change. By collecting light in, for instance, the plus and/or minus first order diffraction modes for display, each pixel appears dark when in the non-diffractive state and light when in the diffractive state.
R. Apte et al, SID 1993, pp. 807-808, "Deformable Grating Light Valves for High Resolution Displays" disclose an arrangement which uses the same diffractive optical effect. However, diffraction is caused by mechanically moving freely suspended under-etched linear reflectors. G. Sextro et al, SID 1995, pp. 70-75, "High-Definition Projection System Using DMD Display Technology" discloses a high brightness projection panel which uses flexible micro-mirrors. The mirrors are controlled so as to deflect light in or out of the display light path.
K. M. Johnson et al, IEEE J. Quantum Electronics, 1993, vol. 29, No. 2, pp. 699-714, "Smart Spatial Light Modulators using Liquid Crystals on Silicon" discloses various techniques for combining liquid crystal devices with silicon integrated circuit technology to form SLMS.